Calcium Carbonate Mineralization: X-ray Microdiffraction Probing of the Interface of an Evaporating Drop on a Superhydrophobic Surface

The liquid/air interface of calcium bicarbonate solution drops was probed by synchrotron radiation microbeam scattering. The drops were deposited on a nanopatterned super-hydrophobic poly(methyl methacrylate) surface and raster-scanned during evaporation by small-angle and wide-angle X-ray scattering. The appearance of about 200-nm-size calcite crystallites at the interface could be spatially resolved at the onset of crystallization. Diffuse scattering from the interface is attributed to a dense nanoscale amorphous calcium carbonate phase. Calcite was found to be the major phase in the solid residue with vaterite as minor phase.